This invention relates to the preparation of mesoporous materials containing a Group IIA element prepared by sol-gel type techniques.
Porous materials play an important role in many chemical processes. Mg, Ba and Ca containing SiO2""s can act as catalysts for base-catalyzed reactions. MgO/SiO2""s are ceramic precursors to enstatite, or forsterite (Matthew B. D. Mitchell et al, Preparation and characterisation of forsterite (Mg2SiO4) aerogels, Journal of Non-Crystalline Solids, 255, 1998, 125-129). BaO/SiO2""s have been reported as components in dental resins and as components for alkali resistant coatings (N. N. Ghosh et al., Synthesis of SiO2-BaO powder by aqueous sol-gel processing for use in dental composite resins, British Ceramic Proceedings 54, Ceramic Films and Coatings, edited by W. E. Lee). CaO/SiO2""s have been used as media for bioactivity studies, as well as precursors for glass materials (I. lzquierdo-Barba et al., In vitro calcium phosphate layer formation on sol-gel glasses of the CaO-SiO2 system, Departmento de Quimica Inorganica y Bioinorganica, Facultad de Farmacia, Universidad Complutense de Matrid, E-28040-Madrid, Spain, Apr. 7, 1999). Controlling the size and distribution of the pores in such materials can assist in attaining desired physical and chemical properties.
Mesoporous materials are commonly prepared using sol-gel techniques followed by freezing-drying or supercritical extraction (R. Portillo et al., Magnesia Synthesis via Sol-Gel: Structure and Reactivity, Langmuir, 12, 1996, 40-44). Both of these techniques can be energy-intensive and require specialized equipment. There is a need for techniques to produce highly mesoporous materials efficiently and at atmospheric pressures.
The invention is directed to a silica-based material made by a process of: (i) dissolving a source compound containing a Group IIA element in a carboxylic acid to form a solution; (ii) adding to the solution obtained in step (i) a silicate selected from the group consisting of Si(OR1)4 and SiR3(OR2)3, where R1 is a C1 to C4 alkyl group, R2 is a C1 to C8 alkyl group and R3 is H, C6H5 or R2, where C6H5 is a phenyl group, to form a gel; (iii) aging the gel product obtained in step (ii) for a time sufficient to incorporate the Group IIA element into the gel; (iv) refluxing the product obtained in step (iii) two or more times in a volatile solvent that is miscible or soluble with the carboxylic acid utilized in step (i); (v) drying the product obtained in step (iv); and (vi) optionally, calcining the silica-based material obtained in step (v). The carboxylic acid can be acetic acid or formic acid, preferably it is glacial acetic acid. The source compound can be a Group IIA alkoxide, acetate, or chloride such as Mg, Ca, or Ba. The reflux solvent can be hexane or ethanol. Optionally silylation is performed on the product obtained in step (iv).
The invention is also directed to a composition of matter including a mesoporous material containing a Group IIA-element and having a pore volume of about 1.1 cc/g to about 3.0 cc/g and having a majority of pores with a pore diameter of greater than about 7 nm. The material preferably has a pore volume of about 1.9 cc/g to about 3.0 cc/g, and a majority of pores with pore diameters between about 10 to about 15 nm. Preferably, all pore diameters are greater than or equal to 2 nm.
The invention is also directed to a process for preparing a silica-based material by: (i) dissolving a source compound containing a Group IIA element in a carboxylic acid to form a solution; (ii) adding to the solution obtained in step (i) a silicate selected from the group consisting of Si(OR1)4 and SiR3(OR2)3, where R1 is a C1 to C4 alkyl group, R2 is a C1 to C8 alkyl group and R3 is H, C6H5 or R2, where C6H5 is a phenyl group, to form a gel; (iii) aging the gel product obtained in step (ii) for a time sufficient to incorporate the Group IIA element into the gel; (iv) refluxing the product obtained in step (iii) two or more times in a volatile solvent that is miscible or soluble with the carboxylic acid utilized in step (i); (v) drying the product obtained in step (vi) to yield a silica-based material; and (vi) optionally, calcining the silica-based material obtained in step (v). The carboxylic acid can be acetic acid or formic acid, preferably it is glacial acetic acid. The source compound can be a Group IIA, such as Mg, Ca, or Ba, alkoxide, acetate, or chloride. The reflux solvent can be hexane or ethanol. Optionally silylation is performed on the product obtained in step (iv).